Synthesis, thermal behavior, and spectroscopic study of the solid nalidixate of selected light trivalent lanthanides
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Solid-state [Ln(nal)3]·nH2O compounds, where Ln represents light trivalent lanthanide (La to Sm, except Pm), nal is nalidixate (C12H11N2O3), and n is the number of water molecules, were synthesized. Characterization and investigation were made by means of complexometry, elemental analysis, powder X-ray diffraction, Fourier transform infrared, near infrared (NIR) and diffuse reflectance spectroscopies, simultaneous thermogravimetry and differential thermal analysis, and differential scanning calorimetry. The dehydration process occurs in a single step up to 453 K. The final temperature of dehydration decreases from Pr(III) to Sm(III), and the thermal stability of anhydrous compounds increases from La(III) to Sm(III) (except Ce), and these behaviors are related to the decrease in the ionic radius of the lanthanide ion. The thermal decomposition of the anhydrous compounds occurs in three, four, or five consecutive steps, with formation of the respective oxides CeO2, Pr6O11, and Ln2O3 (Ln = La, Nd, and Sm) as final residues. The results also provide information concerning the composition and thermal behavior of these compounds. Spectroscopic studies in the UV–Vis and NIR regions provide information about the characteristics 4f–4f transitions for the Pr(III), Nd(III), and Sm(III) compounds, as well as the NIR region characteristic overtone and combination bands of the compounds.